Thursday 24 September 2020

Asteroid 2020 QD passes the Earth.

Asteroid 2020 QD passed by the Earth at a distance of about 10 662 000 km (27.8 times the average distance between the Earth and the Moon, or 7.13% of the distance between the Earth and the Sun), at about 4.45 pm GMT on Thursday 17 September July 2020. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2020 QD has an estimated equivalent diameter of 100-320 m (i.e. it is estimated that a spherical object with the same volume would be 100-320 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 200-17 500 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater roughly 1.2-3.5 km in diameter and devastation on a global scale, as well as climatic effects that would last years or even decades.

The orbit of 2020 QD, and its current position. JPL Small Body Database.

2020 QD was discovered on 16 August 2020 (over a month before its closest encounter with the Earth) by the University of Hawaii's PANSTARRS telescope. The designation 2020 QD implies that it was the fourth asteroid (asteroid D - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that D = 4) discovered in the second half of August 2020 (period 2020 Q).
2020 QD has a 1359 day (3.72 year) orbital period, with an elliptical orbit tilted at an angle of 4.00° to the plain of the Solar System which takes in to 0.65 AU from the Sun (65% of the distance at which the Earth orbits the Sun, and slightly inside the orbit of the planet Venus) and out to 4.15 AU (415% of the distance at which the Earth orbits the sun and more than twice as far from the Sun than the planet Mars). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in March 2017 and the next predicted in January 2032. It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2020 QD is also classified as a Potentially Hazardous Asteroid.
2020 QD also has occasional close encounters with the planets Venus, which it last came close to in February 2017 and is next predicted to pass in January 2084, Mars, which it last cam close to in May 1965 and is next predicted to pass in May 2024, and Jupiter, which it last came close to in Arpil 2019 and is expected to pass again in January 2067. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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